Realizing high-efficiency hydrogen evolution in cost-effective and long-lasting electrocatalysts is critical for global production of clean and sustainable chemical fuels. Here, via modulating the metallic 1T phase in 2H MoS₂ nanosheets, we greatly improved the conductivity and effective active sites for highly efficient electrocatalytic hydrogen evolution. The as-synthesized 1T-2H MoS₂ electrocatalyst with a high 1T-phase content of 50% can significantly increase the charge concentration by an order of magnitude and triple the effective active surface sites, successfully boosting the hydrogen evolution reaction (HER) at a quite low overpotential of 126 mV at 10 mA/cm² and a small Tafel slope of 35 mV/dec. Ultraviolet photoelectron spectroscopy and electrochemical characterization reveal that the valence band edges of 1T-2H MoS₂ are upshifted by 0.15–0.36 eV, which obviously enhances the charge transfer ability of the surface active sites in the basal plane of MoS₂ for high HER performance.